High resolution camera with hardware data compaction

ABSTRACT

A high resolution object handling system serves as an object discrimination - identification by creating an object silhouette. The objects are singulated on a conveyor and scanned by a linear array of CCD units (2048 pixels per inch) at a scan rate of 10 MHz. Pixel transitions corresponding to object edge points are converted to a single count value from a counter which is synchronized with the scanner. A microprocessor with a first in, first out buffer memory needs only a capacity to handle the count value rather than all data from the pixels.

This invention relates to the compaction of data by use of data by useof hardware in connection with the real-time creation of a highresolution silhouette image of an object on a moving conveyor.

BACKGROUND INFORMATION

In the inspection by video equipment of objects being transported on aconveyor, it is required that the image processing be done on a realtime basis to produce the necessary secondary control signals. Variousprior art techniques are disclosed in Ohyama U.S. Pat. No. 4,866,783.

Composite video signals are not required for some applications. It maybe sufficient to have a high resolution silhouette of an objectelevation to determine the object orientation or size. Real timeprocessing of large amounts of data is prohibitive for a feasiblelow-cost system due to the processing time involved and huge memoryrequirements to store all the information customarily used. Usualsolutions to enable high resolution would be to invest in an expensive,faster computer and to add on the required memory.

SUMMARY OF INVENTION

It is an object of the invention to provide a novel method and systemfor the compaction of serial binary image information for reducing imageprocessing time and memory requirements while maintaining the requisitevideo intelligence information.

The method includes scanning a linear array of CCD units that areshadowed by the profile of objects on a moving conveyor producing aunique signal related to the position of at least one edge point of theobject during each scan. Only the unique signal is processed withoutrequiring memory for the signals from all of the scanned CCD units.

Successive scans at intervals shorter than one millisecond allow objectedge points to be determined in the direction of the object movementthereby to form a high resolution silhouette image. The system includescircuits to process a vertically scanned object and to produce a serialbit stream representing the vertical scan. An edge detection circuit isprovided to detect changes in the serial bit stream and trigger transferof instantaneous count values from a synchronized counter into memory.

The invention provides a low-cost solution to the problem of reducingdata handled by a ratio of up to 20:1 from a serial bit stream of fixedtotal length by reducing the number of data bits to be manipulated andstored. A linear array of between about 1000 and 4000 pixels per inchfacing a collimated light source and shadowed by an object on theconveyor as it passes between the light source and the linear array isable to provide a resolution of as little as 0.0005 inches. The pixelscanner and counter circuit are all driven by a central clock oscillatoroperating at frequencies in the range of 1 MHz to 40 MHz and reset atintervals in range of a few hundred microseconds thereby to allowconveyor speeds of several inches per second. Standard off-shelfavailable components may be used and use of a relatively small memorycapacity and inexpensive computer is possible.

These and other objects and advantages will become more fully apparentfrom the claims, and from the description as it proceeds in conjunctionwith the drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagrammatic view of a conveyor system for separating andorienting parts, together with a novel inspection camera and informationprocessor;

FIG. 2 is a block diagram of a camera sensor and related functionalcircuitry for acquiring and storing object silhouette information;

FIG. 3 is an elevation of a conveyor moving surface that is supporting around of ammunition;

FIG. 4 is a group of waveforms taken at scan position 120 as depicted byline 4--4 of FIG. 3;

FIG. 5 is a group of waveforms taken at scan position 800 as depicted byline 5--5 of FIG. 3; and

FIG. 6 is a diagram of a suitable circuit arrangement for hardware thatcan compact the object image intelligence data.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

The present invention is adapted for use with conveyors that move aseries of like objects on a repetitive basis for automated inspection orassembly. The invention serves as a substitute for human inspection ofthe object orientation on the conveyor surface and is adapted to providedata representation concerning a part size that may have a resolution aslittle as 0.0005 inches.

In the illustrated conveyor 10 of FIG. 1, objects 12, 14, 16 rest on asurface 18 that moves in a counter clockwise direction while a tiltedcentral disk rotates at a slower speed to load objects in spacedpositions along conveyor surface 18 in a known manner. The objects 12,14, 16 pass between a camera sensor 22 and a light source 24 after whichthey move downstream to a conventional detector 26 and diverter 28 whichenables reorientation and/or rejection of improperly oriented or sizedarticles. The diverter may of the general type as shown in Dean et alU.S. Pat. No. 4,619,356.

In accord with one feature of the present invention, a camera sensor 22is not a raster scan type, but instead consists of a linear array ofcharge coupled device (CCD) units. The CCD units are aligned to betransverse to the direction of object movement. The linear array of CCDunits thus may be essentially vertical in the case of a horizontalconveyor. The CCD units are aligned in a single column that is one pixelwide and at least about 1000 pixels high. The height of the CCD unitcolumn must be sufficient to span the feature of interest of the object12, 14, 16 on the conveyor 18. For many small objects such as bolts,screwdriver handles, small caliber ammunition and the like, a maximumvariation of the feature of interest may be within a one inch span.

A silhouette image data obtained for certain applications must have a0.0025 inch resolution. The number of CCD units in the one inch columnmay conveniently be about 2000 and advantageously may be 2048. An evensmaller resolution below 0.0005 inches may be obtained with the use ofabout 3000 or 4000 pixels in a one inch column. The linear array of CCDunits may be obtained commercially from Texas Instruments as TC-103-1.The drive circuitry necessary for proper CCD operation and timingdiagrams to provide a sequential scan of the analog voltage signal arecommercially available. The scan rate must provide sufficient time totransfer each pixel charge fully and not allow any charge to accumulatein pixel between reset and the next scan at which time a momentaryvoltage is applied to each of the CCD sensing units.

In the system of the present invention, the light source 24 is locatedacross the conveyor surface 18 to face the CCD units. As an object 12,14, 16 passes between the light source 24 and the camera sensor 22, ashadow is formed on certain of the pixel areas whereas unblocked pixelsare fully illuminated by the light. By use of a collimated light sourcewhich operates through a lens having a shape and size corresponding tothat of the linear array of CCD units forming a camera sensor, a precisepoint on the upper edge surface of the object can be opticallydetermined with great accuracy. Variations in ambient light conditionsare less likely to interfere with operation of the camera sensor when acollimated light source is used.

If the object has a point on the lower edge surface that is positionedabove the conveyor surface, a light beam will be detected atappropriately positioned pixels in the same linear array at a point onthe lower surface which is opposite the detected point on the upperobject surface. Similarly, an aperture in the object which is alignedbetween collimated light source and the camera sensor will producetransitions in the adjacent pixels to provide a manifestation of themarginal edge points of the aperture at successive positions as theobject advances past the camera sensor.

Successive exposures of the camera sensor 22 to each object 12, 14 or 16as it moves along the conveyor path 18 gives successive data inputswhich may be sequentially processed and collectively used to provide asa display, a silhouette of the object before the object reaches thediverter station 28. Object speed on the conveyor may be several inchesper second depending upon the desired resolution. Successive scans maybe provided at 300 microsecond intervals with a 2048 pixel linear arraydriven by a 10 MHz clock. Conveyor speeds up to seven inches per secondmay be acceptable without exceeding the resolution accuracy specified.

The installation as illustrated in FIG. 1 may include also a systemcontrol 30 and control box 32 which are usually physically located nearthe conveyor.

With reference to FIG. 2, a functional block diagram of the camerasensor 22 is illustrated. The vertical column of CCD units 34,consisting of a 2048 pixel linear array in the illustrated embodiment,is connected to receive clocking or timing signals from the clock andsync circuit 35. Clock circuit 35 includes an oscillator running at afrequency of at least about one MHz, and 10 MHz in the illustratedexample, in order to provide pixel scanning in about 200 microsecondsand 100 microseconds for reset operation. The CCD units that arecommercially available are capable of running at clock frequencies ashigh as 40 MHz. Thus, pixel scan during a 300 microsecond sampling scanafter conditioning, is used to produce an analog information signalwhich contains a transition relating to the precise position of an edgepoint on an object or part which is being conveyed.

From the column of CCD units 34 which each functions as a pixel, anoutput signal on lead 36 is in the form of an analog signal voltage (seeFIGS. 4 and 5) containing sequentially obtained voltages of a firstamplitude for shadowed pixels and a second low amplitude for thosepixels receiving light from light source 24. The analog information is aserial bit stream of uniform length and is transferred serially at theclock rate to a voltage follower that serves as an isolation circuit 38and to a black sample and hold circuit 40 which produces a voltage levelreference signal from pixels that are blocked from receiving light. Thisprovides a reference signal which holds the analog signal at acontrolled DC level and may be used as one input to circuitry associatedwith an analog to digital conversion circuit 42.

The output signal on lead 44 is applied to the transition detector anddata compaction circuitry 48 which will be described in connection withFIG. 6. On lead 46, a clock signal from the clocking and sync circuit 35is applied to maintain synchronization between the data compaction unit48 and the scanning means that is part of the charge coupled devicearray 34.

The output signals from the data compaction device 48 on leads 50 is inthe form of a single binary number for each transition from the analogto digital conversion circuit and is applied to the memory 52 whichserves as a buffer to collect all of the data for a particular object12, 14 or 16 on the conveyor surface on a first in, first out basis. Themicroprocessor unit 54, which may be any suitable type that iscommercially available, may start to process the output signals as soonas the memory 52 begins to receive valid object data.

The camera sensor 22 is thus synchronized with a counter in the datacompactor 48 by means of the clocking and sync circuit 35. The memory 52for data buffering may have a 64K or even smaller capacity for objectsof the type mentioned above. As pointed out above, low cost commerciallyoff-shelf available components have a capability to operate up to a 10MHz data rate in a reliable fashion thereby providing a low costhardware product.

With reference to FIG. 3, there illustrated a round of ammunition whichhas a cylindrical cartridge or casing 56 that is supported on a conveyorsurface 18 and a projectile 58. FIG. 4 contains a group of waveformstaken along line 4--4 of FIG. 3 and FIG. 5 contains a group of similarwaveforms taken along line 5--5 of FIG. 3. FIG. 4 waveforms are taken ata position corresponding to scan 120 whereas, the FIG. 5 waveforms aretaken at scan 800.

In FIG. 4, the waveform of the amplified analog signal starts at time 0in a black condition because of the conveyor 18. At pixel 30, whichcorresponds to count 30 in a counter, light is detected thereby startinga negative going digital pulse and a positive going edge detector pulse60. At pixel 100, the lower edge point on the silhouette of theprojectile 58 is effective to block light and create a further edgedetector pulse 62. At pixel 500, the light is again detected, therebycausing a third edge detector signal 64 to be generated. Finally, at thetop of pixel linear array and pixel 2048, the scanner no longer producesa signal and an end of scan transition detector pulse 66 is generated.

A conventional binary counter capable of counting up to at least 2048 atthe clock frequency is synchronized with the scan of the 2048 pixels inthe camera sensor as indicated at the bottom waveform of FIG. 4. Theclock is reset to start at zero as the scan starts so that count valuesof 30, 100, 500 and 2048 are stored in the memory 52 of FIG. 2 asdetermined by the time of occurrence of edge detector pulses 60, 62, 64and 66.

FIG. 5 shows the corresponding waveforms that occur at scan 800. Sincethe lowest point on the cylindrical casing 56 rests on the conveyorsurface 18, the lowest 1499 pixels in the linear array are dark and thefirst transition occurs with pixel 1500, which is aligned with the upperedge point of the cartridge casing 56 at scan position 800.

The edge detector pulse 68 is generated in response to the transition atpixel 1500 and causes the count value of 1500 to fall through the memory52 to its output terminals. A similar edge detector pulse 70 occurs atcount 2048. Thereafter, a master reset pulse is generated. The countersare reset to a zero count by a counter reset signal which issynchronized with the beginning of the next scan of the pixels.

FIG. 6 shows one preferred embodiment for converting the digital signalsof FIGS. 4 and 5 into count values that are supplied to themicroprocessor unit (MPU) 56. The digital signal from FIG. 4, in theform of incoming serial binary bit, is applied to terminal 80 of anegative and positive edge detecting network that detects changes in thebinary state and issues for each positive or negative edge a 50n sec.pulse on lead 82. At a 10 MHz clock frequency, the scanned informationdata and clock counts are separated by 100n sec. The 50n sec. pulse isused to gate on the memory unit 52 (FIG. 2) which includes FIFOregisters 84 as illustrated in FIG. 6. The three binary counterregisters 86 that operate with clock signals on lead 46 are reset by acounter reset signal on lead 88. The count value on leads 50 isconstantly presented to the FIFO registers 84. However, the count valuesare allowed to drop through the FIFO registers 84 only when an edgedetector pulse on lead 82 is present. In this example, the count valuesof 30, 100, 150 and 2048 are stored.

When a count value falls through the FIFO registers 84, the FIFO issuesan output ready signal to MPU 54 on lead 92. When the MPU sees an outputready signal, it issues a shift out signal on lead 94 to FIFO registers84 which releases the count value immediately to the MPU 90. The data atthis point is then coded object image intelligence. This handshakingcontinues throughout the entire scan cycle and sequentially throughoutall scans of a object.

As is evident from the foregoing, for the scan 120, only four countvalues are processed and stored rather than 2048 bits of scaninformation. Other scans such as scan 800 may have only two count valuesthat are processed. The number of scans may be decreased where lessresolution in the horizontal direction is acceptable thereby furtherreducing the processing time. This compaction of data increasesprocessing speed and reduces memory size requirements withoutsacrificing resolution of the silhouette image.

While only a single embodiment has been illustrated, other modificationsand variations will become apparent to those skilled in this art. Theillustrated embodiment has a degree of sophistication which can besimplified for less demanding applications. It is therefore intendedthat the variations and modifications which fall within the scope of theappended claims and equivalents thereof be covered thereby.

We claim:
 1. A method for compacting serial binary kit streaminformation for reducing image processing time and memory requirementscomprising:producing a serial bit stream during a scan interval, the bitstream having at least 1000 bits and a number of binary transitions;connecting each transition into an edge pulse having a duration lessthan the duration of one of said bits; counting bit periods to produce aunique count valve for each bit; and storing only a unique count valvefor each transition in a memory that is gated on by said edge pulses. 2.The method as defined in claim 1 wherein a plurality of bit streamshaving the same length are produced during successive scan intervals andcounting is re-started at the beginning at each scan interval.
 3. Themethod as defined in claim 2 wherein the bit stream information relatesto an object edge point location for use in determining a silhouette ofthe object, said method further comprising:exposing a linear array ofpixels to a source of collimated light: passing said object along a pathto form a shadow on a portion of said pixels; and scanning said lineararray of pixels to produce an analog information signal which varies inaccordance with whether a pixel receives or is shadowed from said sourceof collimated light.
 4. The method of claim 3 wherein binary transitionsoccur at time intervals which correspond to scan times of transitionsoccurring between adjacent pixels which are shadowed and illuminated. 5.A system for determining the position of adjacent points lying along anobject edge comprising:an analog to digital conversion circuit includingmeans to control the amplitude level for digital transition; means forsuccessively scanning a visual image of said object to transfer ananalog information signal relating to an edge point on said object tosaid analog to digital conversion circuit to produce a pulse related toa location of said object edge point; a counter circuit synchronizedwith said scanning means; means connecting said pulse to trigger countinformation from said counter circuit that identifies a location ofdifferent ones of said object edge points in successive scans; a firstin, first out buffer memory; and means for applying to said buffermemory count information limited to that which corresponds to saidobject edge points based on successive scan information thereby toprovide object profile data.
 6. The system as defined in claim 5 whereinthe buffer memory contains object edge information in the form of acount value for each point in the one direction video image scan therebyenabling rapid processing of said buffer memory signals as informationrelating to all of the object edge points is obtained.
 7. The system asdefined in claim 6 together with a conveyor structure for moving aplurality of singulated objects relative to a camera sensor and amicroprocessor unit connected to the output of said buffer memory, andwherein the buffer memory signals relative to a first object on saidconveyor structure are transmitted to the microprocessor beforeinitiating scanning of the next object.
 8. The system as defined inclaim 7 wherein the system further comprises means for detecting thepositions of two aligned points on opposite object edges during eachscan, and means operative during each scan to provide count informationcorresponding to only the positions of each of said two aligned pointsthereby to provide accurate information concerning the spacing said twobetween aligned points on the object without processing analoginformation signal portions that are unrelated to either of said twoaligned points.
 9. The system as defined in claim 8 wherein the objectsmove in a generally horizontal direction, the camera sensor isstationary, said one direction is vertical and the count informationrelates to both size and orientation of an object on said conveyorstructure.
 10. A system for storing information related to anorientation of an object moved by a conveyor in a first direction in amemory circuit connected to receive a plurality of digital signalsrelated to a series of adjacent points on at least one marginal edge ofsaid object comprising:an analog to digital conversion circuit; a singlelinear array of charge coupled devices providing pixels that extendalong a second direction that is transverse to the first direction; asynchronization circuit including means for producing clock signals;scanning means for producing an analog voltage signal from said pixelsoperating in synchronization with said clock signals; means foroutputting said analog voltage signal from said pixels to said analog todigital conversion circuit; an object edge detection circuit coupled toreceive output signals from said analog to digital conversion circuitfor generating a transfer signal at a time during a scan of the pixelsthat is related to detection of an object edge point; a counter circuitoperating in synchronization with said clock signals and said scanningmeans and being reset between successive scans; and means connectingsaid memory circuit to receive a count value from said counter circuitwhich coincides with the time of occurrence of said transfer signalswhereby the count value is the only information stored concerning thelocation of said object edge points.
 11. The system as defined in claim10 wherein said object edge point transfer signal is a pulse that has aduration that is about one-half the duration of output signals from thecounter circuit.
 12. The system as defined in claim 10 wherein thepixels extend beyond two opposite edges of said object and two transfersignals are generated by said object edge detection circuit to identifythe relative positions of points on opposite marginal edges of saidobject and provide a size measurement of said object.
 13. The system asdefined in claim 12 wherein the density of pixels in the linear array isat least about 2000 pixels per inch thereby to provide a sizemeasurements having a resolution at least as small as 0.0025 inches. 14.The system as defined in claim 10 wherein the said transfer signalsgenerated by said object edge detection circuit are connected to opensaid memory circuit to receive an instantaneous count value from saidcounter circuit, and said memory circuit has a storage capacity forstoring only count values relating to edges of said object and isconnected to transfer on a first in, first out basis the stored countvalue information to a microprocessor.
 15. A system for determining asilhouette of an object moving in a first direction comprising:at least1000 pixels aligned in a direction transverse to the moving direction ofthe object to extend above and below the object on the conveyor;scanning means for successively producing an analog signal voltage fromeach of said pixels which signal is applied to an analog to digitalconversion circuit; means for generating a transfer signal connected tothe output of said analog to digital conversion circuit; a countercircuit operating in synchronization with said scanning means and at acounting speed in excess of 1 MHz; a memory connected to said countingcircuit to receive a count value only in response to receipt of atransfer signal whereby the difference between two count values obtainedduring a single scan is related to a dimension of that portion of theobject imaged by said pixels.
 16. The system of claim 15 wherein thememory has a capacity capable of storing in a first in, first out basisall of the count values corresponding to a plurality of points along thehorizontal dimension of the object and the system further comprises amicroprocessor for processing the stored count values for providing aplurality of object measurements that determine the object silhouette.17. The system of claim 16 where in the density of the aligned pixels isabout 2000 pixels per inch along the direction of the object dimensionbeing measured thereby to provide measurements having a resolution atleast as small as about 0.0025 inches.